Old barrel symbolizes nazi nuke failure

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You wouldn't think that a rusty old barrel is much of an attraction. But the one that sits near the entrance of the U.S. National Second World War Museum in New Orleans manages to draw crowds. Why? Because it represents the death knell for Nazi Germany's attempt to make a nuclear weapon.

This particular barrel was one of 29 aboard a ferry crossing Lake Tinnsjo in Norway on its way to Germany. The "Hydro" was sunk by Norwegian saboteurs in 1944 and the barrel languished at the bottom of the lake until archeologists brought it to the surface in 2004. What did the barrel contain to warrant such a major salvage operation? Water. But not ordinary water, it was "heavy water"

Our story begins in December 1938 at the Kaiser Wilhelm Institute in Berlin. Chemists Otto Hahn and Fritz Strassman were following up a piece of intriguing research carried out by Enrico Fermi in Italy. Fermi had bombarded some common elements with neutrons and discovered that they would sometimes be converted into other elements, although these were always close in mass to the originals. But when Hahn and Strassman subjected uranium to neutron bombardment, they found a result they could hardly believe. The reaction mixture contained barium, an element with about half the mass of uranium.

"Perhaps you can suggest some fantastic explanation," Hahn excitedly cabled Lise Meitner, the physicist he had worked with for many years before she was forced to flee Germany for Sweden because of her Jewish heritage. Meitner did not disappoint. Perhaps, she suggested, the uranium atom had been "split" apart. At that moment, the concept of nuclear fission was born. Further experiments by Hahn, Strassman and Meitner's nephew Otto Frisch not only confirmed the stunning results, but also revealed that such nuclear fission was capable of releasing tremendous amounts of energy. The military implication of the research became obvious on both sides of the Atlantic.

The German "uranium project" was led by theoretician Werner Heisenberg and army physicist Kurt Diebner. It was Heisenberg's calculation that slower moving neutrons would cause the uranium nucleus to split more readily that focused attention on "heavy water," a substance capable of slowing down neutrons. Furthermore, slow neutrons could also be captured by the uranium nucleus, which would then be converted into plutonium, another fissionable element.

As virtually every student knows, a molecule of water is made of two atoms of hydrogen and one of oxygen. Good old H2O. But not every hydrogen atom in the universe is alike. Some hydrogen atoms are heavier because they have an extra neutron in their nucleus. We refer to these as an "isotope" of hydrogen, and use the specific term "deuterium (D)." When a water molecule has two deuterium atoms instead of two hydrogen atoms, we have "heavy water." Since the natural abundance of deuterium is low, only 1 in every 4,500 or so water molecules is "heavy."

By 1933, Gilbert Lewis at Berkley had a method of separating heavy water from ordinary water. His technique relied on the fact that under the influence of an electric current, a hydrogen-oxygen bond is broken more readily than a deuterium-oxygen bond. So when a current is passed through water, H2O is broken down more readily than D2O, leaving the sample enriched in D2O, or "heavy water."...

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